The present invention relates to commonly controlled multiple electronic switches and, more particularly, to controlled electronic switches in which electrical power for the control arrangement is provided from external load circuits connected to one or more of such switches.
There are many electrical circuit situations in which events in various separate circuits are to be coordinated with one another through there being a more or less simultaneous switching event occurring in each such circuit. If there is not to be actual simultaneous occurrence, at least there is often a requirement that the switching events in one circuit occur approximately simultaneously with those in some of the separate circuits and within a fixed time of switching events occurring in others of those separate circuits.
This desire can be given effect by the use of a set of electrical switches under the control of a common control arrangement. While such functions have often been provided in the past through the use of electrically operated mechanical relay switches, there are currently many situations in which the limitations of such relays are desired to be avoided through the use of electronic switches. Such limitations to be overcome by the use of electronic switches include limits on the speed of switching, limits on the volume of space required for the controlled electronic switches, available power, reliability of operation in adverse environments, etc.
The switching characteristic usually required of such electrical switches is that they either be normally open or normally closed. In a normally open condition or state, the switch provides a relatively low conductivity between its terminals to the point of being an open or nearly open circuit between the switching terminals of the switch involved. In a normally closed state, the switch provides a relatively high electrical conductivity between its terminals to the extent of approaching a short circuit between the switching terminals of the switch involved. A switching command from the switch controller will result in a normally closed switch taking on approximately the characteristic described above for the normally open switch and vice versa. In some situations, a change of state from normally closed to open, or from normally open to closed, is to result in the new state continuing without regard to the subsequent status of the controller commands, and in other situations the new state is to continue until the controller commands otherwise.
Electrical power to operate the control arrangement for the switches in many situations will be available only from one or more of the external load circuits to which the electronic switches are connected rather than being independently available to this control arrangement. If the external power is available to an electronic switch that is normally open, the closing of that switch to become a near short circuit will markedly reduce the voltage available to the controller from the external source as that electronic switch provides a high conductivity path between its terminals. Thus, a controlled electronic switch is needed which can operate with an external load circuit supplying power thereto even though the switch for this external circuit must be closed at times. In addition, a controlled switching circuit should permit other electronic switches under such control to be operated independently of current flow conditions in such an external load circuit supplying power. Further, each of the external load circuits connected to the controlled electronic switch, in so operating, should remain essentially electrically isolated from one another, at least each being prevented from drawing any significant current from any of the others through the switch itself.